In the Surface and underground combined mining scheme of the primarg design in Huidong Lead Zinc Mine,it was decided to start underground mining at 1980m tevel under the open pit bottom by downward slice and drift mining with cemented filling and gradually form a 36m thick separation pillar,howerer this scheme was not suited to the actual situation of the mine already.This paper discussed five modified schemes and considered that the initial underground mining area selected outside the open pit bottom was able to expand open pit mining range,reduce the construction cost of separation pillar and eliminate interfernce between open mining and underground mining.